Safety device



NOV. 19, 1935. I N LEV|N 2,021,454

SAFETY DEVICE Original Filed Oct. 14, 1926 15 0 7 14W: l o

Patented Nov. 19, 1935 UNITED STATES PATENT OFFICE SAFETY DEVICE of Ohio Substitute for application Serial No. 141,657,

October 14, 1926. 1935, Serial No. 932

1 Claim.

The present invention relates to safety devices of. that class which is adapted for association with an enclosed casing of an electric motor adapted to be used in a gaseous mine for the automatic isolation of said motor from an external source of energy supply under conditions occasioning variations in the atmospheric pressure within the casing due to explosions of gas within said casing.

The especial object of this invention is to provide an automatically acting device actuated by an explosion within a motor casing to isolate the power mechanism within said casing from an external source of energy supply.

The means whereby I attain this object are fully set forth in the following specification and illustrated in the accompanying drawing wherein is shown a substantially totally enclosed electric motor adapted to use in the gas charged atmosphere of a coal mine, equipped with the devices of my invention, certain parts being broken away to disclose a sectional view of my improved safety device.

The electrical motors adapted to use within coal mines subject to the accumulation of gas in explosive quantities are commonly enclosed in casings intended to exclude explosive gases from such parts of the apparatus as are subject to the formation of electric arcs such as are caused by commutator or slip ring brushes. Exposure to a gas charged atmosphere for protracted periods of time produce a gradual intrusion of gas to the interior of the casing. Such intrusion is accelerated by the frequent changes of temperature of the apparatus incident to its operation. Such casings have, therefore, been designed to withstand internal explosion and to prevent the transmission of the resulting flame to the external atmosphere of the mine. The gradual deterioration of the casing resulting from such internal explosion tends to reduce the reliability of protection afforded by the casing necessitating careful supervision of its use.

As here illustrated, the motor comprises a field frame I to the ends of which are attached bearing housings 2 and 3 having journal bearings in which the armature 4 is rotatably mounted. At one end, the armature shaft 5 projects beyond the housing 2 for connection with the devices which are to be actuated, in the usual and well-known manner. The bearing housings 2 and 3 are shaped to cooperate with the field frame I to form a substantially totally enclosed casing by which the explosive gaseous atmosphere of the mine is excluded from contact with such parts of the apparatus as are subject to the formation of elec- This application January 8,

tric arcs such as the commutator or slip ring brushes. Exposure of such a casing to a gaseous atmosphere for a protracted period of time results in a gradual intrusion of gas to the inside of the casing, and this intrusion of. gas is accel- 5 erated by the frequent changes of temperature of the apparatus during its operation. It is customary to construct such casings of suificient strength to withstand the strain created by the explosion of the accumulated gas within the casing by the above mentioned electric arcs, and the parts are so designed that the flame resulting from such an internal explosion will not be transmitted to the surrounding atmosphere. It has been found, however, that repeated internal explosions tend to the deterioration of the joints between the various elements of the casing, thereby reducing the protection afforded by the casing. Due to this gradual deterioration of the casing, it is important that the apparatus should be carefully 20 inspected after each internal explosion before the re-admission of current to the circuit of the motor. To insure against the unauthorized re-admission of current, I have provided a safety device comprising the chamber 6, preferably formed in the 25 metal of the field frame, and within this chamber 6 I have mounted a circuit interrupting switch comprising a blade I hinged at one end to the binding post 8 and adapted to be brought into contact with the terminal 9 and to be held in that contact by the action of gravity. The binding post 8 is connected by a suitable conductor cable Ill with a source of electric current supply, and the terminal post 9 is connected by a conductor H with the circuit within the casing. Positioned beneath the switch blade 1 is a piston l2 which is reciprocable in a cylinder !3 communicating with the interior of the motor casing in such manner that pressure caused by an explosion within said casing will move the piston 12 outwardly, lifting the switch blade I away from the terminal 9, thereby cutting off the supply of electric current from the circuit within the motor casing.

Positioned adjacent the free end of the switch blade I is a spring pressed latch [4 adapted to engage the blade I when it is lifted away from the contact post 9, and to prevent its re-establishing that contact until released by the use of a key I5 in the custody of. the person charged with the duty of inspection of the apparatus, and who is authorized to re-establish its connection with the source of current supply.

This application is a substitute for my application Serial No. 141,657 filed October 14, 1926.

It is to be understood, however, that the mechclosing said passage and normally maintained in a position from which it is movable as the result of an explosion in said casing, a switch controlling current supply to said motor and disposed and isolated in said chamber, said switch being normally maintained in closed position, means for transmitting to the switch to open the same movement of the movable member caused by an explosion in the casing, and means for securing the thus opened switch in open position against unau- 10 thorized restoration.

NILS D. LEVIN. 

